Try a simple test. Get some vitamin C tablets, crush them and put them in a sock. Place the sock on one of the stains for two or three minutes and then remove it. Rub gently if you can manage it. If the stain goes away in that spot, or reduces noticably, then you can do an ascorbic acid treatment to remove the stains.
You can also try the same kind of thing with a trichlor tablet and see one minute of that makes any difference. Try the vitamin C first however.